User Custom Fields

Is it possible to add additional fields to the Add User form that can then be displayed within the View/Edit Users page?

In the default configuration a user can have an email address added to their account. However, here is no option to add a telephone number against the user's name which seems strange.

The Edit Custom Properties screen does appear not provide a mechanism to do this, as the list of Artifact Types does not include a User Information or similar option.